Stall warning device



Oct- 5, 1948. R. H. UPsON Re. 23,042

STALL WARNING DEVICE Filed Aug. 25, 1947 W mmm INVENTOR RALPH H. UPSON "Y y A TORNEY Resaued October 5, 1948` Re.` 23,042', L

UNITED STATES PATENT vori-ice Original No. 2,406,719, dated August 27, 1946, Se-

rial No. 513,241, December 7, 1943. Application i'or reissue August 25, 1947, Serial No. 770,362

(ci. zap-ss) 12 Claims. 1 This invention relates to a stall warning device for aircraft, and. in particular, it relates to a stall warning device which functions by reason of the movement of the air pressure lines at the leading edge of an aircraft Wing. More particularly, the invention relates to a device applicable for associ-ation with the leading edge of an aircraft wing for producing an audible and/or visible ysignal upon approaching a stall as a result of a high angle of attack.

Heretofore, it has been general practice for pilots to depend upon air speed indicators and their lown observations or senses in order to determine the approximate point of approach of a stall. Some instruments have been devised to warn the pilot of an approaching stall. However, devices that are available are objection-able in many respects. For example, .some only warn that a stall is actually in progress; others suiler from unreliability due to dependence on air speed. Some employ outwardly projecting mechanisms which, 4because of such features, constitute obstructions which may be bent or otherwise injured, thus impairing fthe accuracy of the device. Furthermore, such outwardly projecting portions permit the accumulation of .ice thereon, or are subject for encounter with various foreign matey rial such as sand, animal life, or the like. Also,

most exterior attachments placed on aircraft and particularly in the vicinity of the wing are objectional from the standpoint of interference with proper air ilow.

In accordance with the practice' of my invention I have provided a simple dependable stall warning device which is particularly applicable for installation within the interior of an aircraft wing, thu-s avoiding all exterior interferences. In general, the invention comprises a tubular element having an opening at the leading edge portion of an aircraft wing and extending yto a cha-rnber enclosing a membranous diaphragm. 'This diaphragm supports an electrical contact which is operable upon movement of the slack diaphragm due to movement of the stagnation point at the leading edge of the w'ing. The electrical contact as thus established results in an audible and/or visible signal inthe vicinity of the pilot.

Among the advantages of my invention are, to provide a stall warning -device which is unitary in construction; economical of manufacture; free from outwardly projecting portions; positive in operation; and, .sensitive in operation in com-bination with -a relatively large movement of con- .tact points whereby uncertainty of operation caused by vibration is eliminated. Other advantages of the invention are oase of installation,

serviceability,y simplicity of structure, and reduction of moving elements. The construction of the device provides for removal oi water or condensa-V tionand permits the application of heating means to prevent ice formation at fthe intake end of the device. A single size device is applicable for use regardless of the size or shape of the airfoil section of the wing, it merely being necessary to locate the intake end of the device on the leading edge of :the wing in proper relationship with the stagnation point in advance of the angle of stall.

These and other objects and advantages will appear more fully in lthe following detailed description when considered in connection with the accompanylngdrawing, in which:

Figure 1 is a side elevation-al view in section, of an embodiment of my invention;

Figure 2 is a side-'elevational view of an embodiment of my invention in combination with a diagrammatic view or an electrical system associated therewith; and

Figure 3 is a perspective view of details of the electrical contact means employed in the device of my invention.

' With reference to the drawing, and in particular .to Figures 1 and 2,i I show an embodiment, in I the form of 4a stal] warning device, comprising, in general, an attachment II to be secured to the leadingedge of an aircraft wing, and a housing I2 adapted to retain means for forming an electrical contact due to a change in pressure within the housing.

The attachment Il comprises a main body I3 having a flanged portion I4 at its foremost end, and an aperture {5 extending through the -body I3. Projecting from the body I3 and in an upwardly angular position is -a tubular portion I6, the aperture of which forms a continuation of the aperture I5. Another portion l1 extending downwardly from the body I3 includes a chamber I8 also communicating with the main aperture I5. Ihe downwardly extending portion I'I is provided with an end enclosure I9 through Wh'ich there is a small aperture 20. Since the principal aperture I5 is open to -the leading edge of an aircraft wing, there is a possibili-ty `that water or moisture may enter such aperture. Therefore, the chamber 'Il which extends downwardly from the aperture I5 functions to collect such water or condensation and allow it to drop out through the small opening 20. It is necessary to maintain -the opening 2li a relatively small size so that it will not interfere with the pressure operation of the device. I have found that good results are obtained by limiting the size of the ,penini 22 to approximately .'0'15" in diameter, or a size in area of about 1/:3 of the area of the aperture i5.

The reference character 2| designates the skin bf the leading portion of lan aircraft wing. The flanged portion Il of the 'attachment Il is curved' s that it will conformrsubstantially to the shape of the skin 2| at the leading edge of an aircraft wing. Internal threads 22 are provided in the 1 body I3 adjacent to the flanged portion Il. An

externallythreaded tubular member 23 having a head portion l24 is adapted to be threaded in complementary engagement with the body I3 in a manner so as to clamp the attachment il in tight relationship with the skin 2|. The opening within the tubular member 22 is in alignment with the aperture I5, thus forming a direct comtion Il.

A rubber or ilexible tubing 2Irlconneets the tubular portion Il with a tubular adapter 2l associated with the housing i2. In general, the

i housing I2 comprises an upper case 21 and a lower case 23 secured together by means of machine bolts 2-2. The cases 21 and 2l are formed so as to provide annular cavitiesJ 2li and 3l, respectively. An aperture 32 forms a communication between the cavity 30 and the tubularv adapter 28, thus forming a complete line of communication to the atmosphere from the leading ledge of an aircraft wing to the tubular portiirn, is held in place by the machine screw Il taiiis the nut Il in spaced relationship with the case 21. Wires l2 and I3 engaging with the bolts ll and respectively, extend to the electrical system, hereinafterdescribed. By this arrangement of contacting points, it is merely necessary for the contact disc 3l to engage any two adjacent contact points 4I, 4I, 42 or 42 in Yorder to complete arcircuit between wires 52 and 32.

A diagram of the electrical system is shown in Figure 2. The wires l2 and |i3` lead to a conventional relay i4. and abattery 5B is connected in the line of the wire l2. Also, a ilxed condenser lies betweenthe wires 52 and 53. The wire I2 extendsdirectly'to a horn I1. Instead ,of a horn it is to be understood that a bell, buzzer,

-or other electrically operated audible signal may' tion to the audible signal 31, thereris provided a mally induced within the wing. A bracket 34 ex'- tends from the lower case 23 providing means for the attachment of the inlet to a spar II (Figure 2) or other structural member within the wing l of the aircraft.

Clamped between the upper and lower cases 21 and 22 is a ring3l to which is secured a slack diaphragm 31. The diaphragm 31 is preferably cemented to the ring 3i in order to maintain the diaphragm in proper desired position and to facilitate its assembly with the housing i2. The diaphragm 21 is formed A.of a thin sheet or film of exible, preferably slack, material of such nature that it will readily flex upon a change of air pressure, particularly a reversal of pressure betweenits two surfaces. The diaphragm 31 may be composed of a thin sheet of rubber, or synthetic rubber. or other materials such as leather or treated fabric. The diaphragm should be light but impervious to air. or substantially so, and capable of 'retaining a suitable exi-bility under conditions of moisture or extreme cold. Positioned centrally of the diaphragm ,.21 is a metallic disc 33 cemented to the diaphragm 31 f and functioning as an electrical contact member.

This disc 23 is relatively light in weight, and I have found that good results have been obtained by forming a disc from brass or copper shim stock of a thickness `of approximately .0025" to .014".

Concentrically with the disc 23 is an electrically insulating disc 3f! supporting electrical contacting points l0, Il, 42 and l2 (Fig. 3). The. points 'll and 4|y form, in eifect, the heads of bolts Il and I3, respectively, attached by means of nuts Il to the upper case 21. These two points 4I and 4I are, therefore, grounded directly to the metallic case 21. 'Ihe contact points |2and '43 ,are joined together by a metallic bar l1 which, in

visual signal l0 in the form of a light bulb. This light bulb connects directly with the wire 52,

and with the wire 5I at a point between the relay Y stagnation point at the leading -edge of the wing so that the oriilce will lie in a positive pressure zone. Under such conditions, the slack diaphragm 2,1 will lie in its lowermost position, as illustrated in Figure l of the drawing. Even if conditions are such as to produce a neutral pressure, the Idiaphragm 21 will still lie in a normal relaxed position because of gravity acting` upon the diaphragm and, the contact disc 38. However, vin Athe event the angle of attack of the wing becomes such as to approach a stall, the pressure v lines at the leading edge of the wing change so as to produce a negativepressure-zone at the oriflce'position. As soon as anegative pressure is reached at the leading edge orifice, the slack diaphragm is caused to move upwardly until the contact disc engages with two or more of the contact points 30, Il, I2 or I2. This action com- 'pletes an electrical circuitwhich functions.

through the relay il to cause both an audible sound by means of lthe horn 51, and a visual signal by means ofthe light bulb 60.

It will be noted that the aperture 33 in the vlower case 23 opens the cavity 3l to the prevailing atmosphere thus allowing the diaphragm 21 to move upwardly due to the negative pressure within the cavity 3l. In order to complete an electrical `circuit between the contacting disc 23 to vibration, warping, misalignment of parts, or a very slight momentary reduction of pressure within the cavity Il. To attain the advantages of this condition, I have found it essential to maintain the contacting elements a distance of at least one-eighth oi' an inch apart, preferably one-quarterinch apart.

In certain cases, such as during the' initial start of a take-ofLor toward the end of a landing, the stalling angle of the planewill have bee-n reached and the audible signal will occur. llli/hen such an expected occurrence takes place, the pilot may, if he so desires, operate the pushbutton 59 so as to break the circuit leading to the audible signal. This push-button does not cut'oi the visual signal. 'I'he advantage of the push-button 59 is merely to cut off the audible signal at such time that instructions may be given the pilot from an` air field control tower. This temporary disconnection of the audible signal in no way interferes with the functioning of the visual signal during periods wherein a stall is likely to occur.

As thus described, it is believed apparentvthat I have provided a'novel and unique device for automatically signalling the pilot upon an approaching stall, and while I have described a preferred embodiment of my invention, it is to be understood that it is susceptible of those modiflcations which appear obviously within the spirit of the invention and as appeari-ng within the scope of the appended claims.

Having thus described my invention, what I claim and desire to protect by Letters Patent, is:

1. In an airplane angle-of-attack indicator, a

conduit having an open end adapted for engage-I ment with the leading edge of an airplane wing, a. rigid casing communicating with the conduit, a flexible slack impervious diaphragm supported by the casing and dividing the casing into separate compartmentameans carried by the casi-ng for actuating a signal, and means carried by the diaphragm for operating said actuating means,

v an upwardly inclined sleeve communicating with said diaphragm being dependent upon its gravitational weight to maintain the means carried by the diaphragm -normally out of actuating relationship, the communication between said casing and conduit being directed to one compartment whereby a reduced air pressure at the open end of said conduit vfunctions to actuate the diaphragm.

2. In an airplane angle-of-attack indicator, a conduit having an open end adapted for engagement with the leading edge of an airplane wing, a downwardly extending tubular member communicating with the conduit and having a relatively small opening at the lowermost portion thereof, a rigid casing communicating with the conduit, a iliible slack impervious diaphragm supported by 'the casing and dividing the casing into separate`compartments, means carried by the casing for actuating a. signal, and means carried by the diaphragm for operating said actuating means, said diaphragm being dependent upon its gravitational weight to maintain the means carried by the diaphragm normally out of actuating relationship, the communication between said casing and conduit being directed to one compartment whereby a reduced air pressure at the open end of said conduit functions to actuate the diaphragm.

3. In an airplane angle-cf-attack indicator, a'. conduit having an open end adaptedfor engagement with the leading edge of an airplane wing,

the conduit, a rigid casing communicating withthe sleeve. a flexible slack impervious diaphragm supported by the casing and dividing the casing into separate compartments, means carried by the casing for actuating a signal,V and means carried by the diaphragm for operating said actuating means, said diaphragm being dependent upon its gravitational weight to maintain the means carried by the diaphragm normally out of actuating relationship, the communication between said casing and conduit being directed to one compartment whereby a reduced air pressure at the open end of said conduit functions to actuate the diaphragm.

4. In an airplane angle-of-attack indicator, a conduit having an open end adapted for engagement with the leading edge of an airplane wing, a downwardly extending tubular member communicating with the conduit and having a relatively small opening at the lowermost portion thereof, an upwardly inclined sleeve communipendent upon its gravitational weight ,to maintain the means carried by the diaphragm normally out of actuating relationship, the communication between said casing and conduit being directed to one compartment whereby a reduced air pressure at the open end of said conduit functions to actuate the diaphragm.

A 5. In Ian airplane angle-of-attack-indicator, a conduit having an open end adapted for engagement with the leading edge of anairplane wing, a downwardly extending tubular member communicating with the conduit and having a relatively small opening at the lowermost portion thereof, said small opening having an area, in the order of lf2, of the area of they conduit opening, a rigid casing communicating with the conduit, a flexible slack impervious diaphragm supported by the casing and dividing the casing into separate compartments, means carried -by the casing for actuating a signal, and means carried by the diaphragm for operating said actuating means, said diaphragm being dependent-upon its gravitational weight to maintain the means carried by the diaphragm normally out of actuating relationship, the communication between said ye'asing and conduit being directed to 'one compartment whereby a reduced air pressure at the open end of said conduit functions to actuate the diaphragm.

6. In an airplane angle-of-attack indicator, a conduit having an open end adapted for engagementwith the leading edge of an airplane wing, a rigid casing communicating with the conduit. a flexible slack limpervious diaphragm supported by the casing and dividing the casing into an upper and a lower compartment, electrical contact means carried by the casing within the upper compartment, and a metallic member carried by the diaphragm and movable with the diaphragm for engagement with said contact means, said diaphragm being dependent upon its gravitational weight to maintain the means carried by the diaphragm normally out of actuating` relationship, the communication between said casing and conduit being directed to the upper compartment whereby a reduced air pressure at the ment withthe leading edge of an airplane wing,v

a rigid `casing communicating with the conduit, a flexible slack impervious "diaphragm supported by the casing and dividing the casing into an upper and a lower compartment, the lower compartment of the casing having an opening there-1 through to the prevailing atmosphere, electrical contact means carried by the casingwithin the upper compartment, and a metallic member carried by the diaphragm and movable with the diaphragm for engagement with said contact means, said diaphragm being dependent upon its gravitational weight to maintain the means carried by the diaphragm normally. out of actuating relationship, the communication between said casing and conduit being Adirected to the upper compartment whereby a reduced air pressure at the open end'of said conduit functions to actuate the diaphragm.

8. In an airplane angle-of-attack indicator, a conduit having an open end adapted for engagement with-the leading edge of an airplane wing, a rigid casing communicating with the conduit, a flexible slack impervious diaphragm supported by the ,casing andv dividing the casing into an upper and a lower compartment, said diaphragm being freely flexible and substantially impervious rto passagev of air therethrough, electrical contact Y means carried by the casing within the upper compartment, and a metallic member carried by the diaphragm and movable with the diaphragm for engagement with said contact means, said diaphragm being dependent upon its gravitational weight to maintain the means carried by the diaphragm normally out of actuating relationship, the communication between said casing and conduit being directed to the upper compartment whereby a reduced air pressure at the open end of said'conduit functions to actuate the diaphragm.

9. In an airplane angle-of-attack indicator, a conduit having an open end adapted for engagement with the leading edge of an airplane wing, a rigid casing communicating with the conduit, a flexible slack impervious diaphragm supported by the casing, Yand dividing the casing into an fupper and a lower compartment, said diaphragm being held in a normally horizontal 'position whereby at equalized pressure in both compartments the diaphragm` assumes a slack position within the lowermost compartment, electrical contact means carried by the casing within the upper compartment, and a metallic member carried by the diaphragm and movable with the upper compartment, 'and a metallic member cardiaphragm for engagement with said contact r means, said diaphragm being dependent upon its gravitational weight to maintain the means c-arried by the diaphragm normally out of actuating relationship, the .communication between said casingand conduit being directed to the upper compartment wherebyga reduced air pressure at the open end of said conduit functions to actuate the diaphragm. l

10. In an airplane angle-of-attack indicator, a conduit having an open end adapted for engage- 8 ment with the leading edge of an airplanewing, a rigid casing communicating with the conduit, a ilexible slack impervious diaphragm supported by'the casing and dividing the casing into an upperand -a lower compartment, said diaphragm being freely flexible and substantially impervious to passage lof air therethrough, said diaphragm being held in a normally horizontal position whereby at equalized pressure in' both compartments the diaphragm assumes a slack position within the lowermost compartment, electrical contact means carried by the casing within' the ried b'y the diaphragm and movable with the diaphragm for engagement with said contact means, said diaphragm being dependent upon its gravitational weight to maintain the means carried by the diaphragm normally out of actuating relationship, the communication between said casing and conduit being directed to the upper compartment whereby a reduced air pressure at the open end of said conduit functions to actuate tl diaphragm. V v

11. In an airplane angle-of-attack indicator, a conduit having an Open end adapted for engagement with the leading edge of an airplane wing, a rigid casing communicating with `the conduit, a flexible impervious diaphragm supported by the casing and dividing the casing into an upper and a lower compartment, electrical contact means .carried by the casing within the upper compartment, and a metallic member carried by the dia.- phragm and vmovable with the diaphragm for engagement with said contact means, said diaphragmbeing dependent upon its gravitational weight tognaintain the means carried by the diaphragm normally oui; of actuating relationship, the distance between the contact means and the metallic member being at least 1A; inch, the communication between said casing and conduit being directed to the upper compartment whereby `a reduced air pressure at the open end of said conduit functions to actuate the diaphragm.

12. In an airplane angle-of-attack indicator, a

rigid casing. a flexible slack impervious diaphragm positioned within the casing and dividing the casing into two compartments, communicating.

means extending from one compartment to a pressure zone at the exterior of an airplane wing,

v communicating means extending from the other compartment to a different pressure zone, and means associated with said diaphragm for operating a signal upon actuating of the diaphragm, said diaphragm being dependent upon its gravitational weight to maintain theI means carried by the diaphragm normally out of actuating relationshi-p.

RALPH H. UPSON.

REFERENCES CITED The following references are of record in the file of this patent: I

UNITED STATES PATENTSl Kcusman June 11, 1940 

